# RxMarbles vs 21 Sharp

The clearest difference is in-app purchases: RxMarbles at none against 21 Sharp's 1. RxMarbles also leads on ratings volume (16 vs 1) and iOS requirement (9.2 vs 17.0). On price, rating, ads and device support there is nothing between them.

Both are free to download. 21 Sharp sells 1 one-off in-app purchase. RxMarbles asks for nothing beyond the download.

On the App Store both sit at effectively the same score — 4.9 for RxMarbles against 5.0 for 21 Sharp. That said, the two scores are not equally well evidenced: RxMarbles has 16 ratings behind it against 1, so its average is the more settled of the two.

## The numbers

| Metric | RxMarbles | 21 Sharp |
| --- | --- | --- |
| Price | Free | Free |
| Rating | [4.9 (16 ratings)](https://appshunter.io/ios/app/rxmarbles/id1087272442/reviews) | **[5.0 (1 ratings)](https://appshunter.io/ios/app/21-sharp/id6757319502/reviews)** |
| Number of ratings | **16** | 1 |
| Positive reviews | 84.0% of reviews | — |
| In-app purchases | **No** | Yes |
| Ads | No | No |
| Update frequency | Every 4 months | — |
| Monetization | **Free** | Free with in-app purchases |
| Size | 21 MB | 1 MB |
| Requires iOS | **9.2** | 17.0 |
| Devices | **iPhone, iPad, iPod** | iPhone, iPad |
| Age rating | 4+ | 12+ |
| Developer | [AnjLab](https://appshunter.io/developer/501327862) | [busyslacker llc](https://appshunter.io/developer/1576079901) |

## What reviewers say

### RxMarbles

[App page](https://appshunter.io/ios/app/rxmarbles/id1087272442)

Visualize and understand ReactiveX observable sequences with interactive diagrams. This educational tool helps developers grasp complex asynchronous programming concepts by illustrating event-based data streams and composition operators.

**Highlights:** Interactive observable diagrams, Visualization of event streams, Demonstration of composition operators, Educational tool for asynchronous programming, Explains observer pattern extensions

**Features:** macOS Compatibility

**In-app purchases:** none


### 21 Sharp

[App page](https://appshunter.io/ios/app/21-sharp/id6757319502)

Master blackjack strategy and card counting with this professional-grade trainer. Learn optimal plays, practice counting systems, and track your progress with realistic simulations and reference guides. Reduce the house edge and gain a competitive advantage.

**Highlights:** Basic strategy training, Card counting drills (Hi-Lo), Realistic practice table, Reference guides, Progress tracking and achievements

**Features:** macOS Compatibility

**In-app purchases (1)**

| Purchase | Price | Billing |
| --- | --- | --- |
| 21 Sharp Premium | $2.99 | one-time |


## Frequently asked questions

### Is RxMarbles free?

RxMarbles is free to download, with no in-app purchases.

### Is 21 Sharp free?

21 Sharp is free to download, with in-app purchases available.

### Which has better reviews, RxMarbles or 21 Sharp?

21 Sharp is rated higher. RxMarbles averages 4.9 out of 5 from 16 ratings, while 21 Sharp averages 5.0 from 1 ratings.

### Do RxMarbles or 21 Sharp have ads?

Neither RxMarbles nor 21 Sharp shows ads.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*